Device For Purifying Exhaust Gases Of An Internal Combustion Engine

ABSTRACT

A device for purifying exhaust gases of an internal combustion engine has a particle filter, which is provided with a catalytically active coating. The catalytically active coating includes a supporting material and an iron-containing material, which is joined to the supporting material and is present on at least the surface of the same. The supporting material is an aluminosilicate or a silicon oxide.

FIELD OF THE INVENTION

The present invention relates to a device for purifying exhaust gases of an internal combustion engine. In addition, the present invention relates to an exhaust system for an internal combustion engine.

BACKGROUND INFORMATION

German Published Patent Application No. 37 16 446 describes a catalytic diesel particulate filter, which has a catalytically active coating of metallically doped zeolite. The zeolite is preferably loaded with a metal of group IB, IIB, VB, VIB or VIIB of the periodic system or a combination of the same, nickel, copper, manganese, vanadium, silver, or a combination of the same being preferably used.

In the case of this known filter, it is problematic, however, that the desired effect only sets in when a reducing agent is added, which, however, constitutes a relatively high degree of expenditure. A further disadvantage of this known particle filter is the fact that NO molecules contained in the exhaust gas are only converted to N₂ above a temperature of 400° C., which makes it necessary to either situate this particle filter very close to the engine or generate high temperatures in the exhaust pipe.

German Published Patent Application No. 37 31 889 describes a diesel particulate filter, which has a filter element as a supporting material for a catalyst manufactured using at least one metallic oxide. The supporting material is made of a ceramic body or dross, e.g. metallic-oxide, body whose pore surfaces are coated throughout with one or more metallic oxides of the groups Ib, Vb, Vib, VIIb, or the Fe group. However, the efficacy of this particle filter with regard to decreasing NOx is also not satisfactory.

In the case of methods and devices for exhaust-gas purification known from the general related art, an additional reducing agent, such as urea or a hydrocarbon, is often necessary to achieve the conversion of NO_(x), which is associated, however, with additional outlay and higher costs.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a device for purifying exhaust gases of an internal combustion engine, which even exhibits a very good purifying efficacy at relatively low temperatures, and in the case of which the need for an additional reducing agent is eliminated.

It was unexpectedly determined that an iron-containing material in the form of a catalytically active substance, which is joined to the supporting material and present on the surface of the same, has a very good efficacy with regard to the conversion of the exhaust gases. Thus, it was able to be determined that the composition of the catalytically active coating according to the present invention induces nitrogen oxides to react with the soot particles present in the exhaust gas, reduction of NO_(x) to N₂, i.e. nitrogen formation, already having been detected at temperatures of app. 220° C., and almost no more harmful NO molecules being contained in the exhaust gas leaving the device, and the need for an additional reducing agent being eliminated.

In this context, the soot particles contained in the exhaust gas are retained at the particle filter in a manner known per se and thus prevented from leaving the exhaust pipe in which the device of the present invention is preferably installed. At the same time, the soot particles retained at the pores of the particle filter are used for the above-described reduction of the nitrogen oxides, which means that the amount of soot increases much less sharply than in the case of known particle filters, and accordingly, regeneration of the same is necessary considerably less often. In addition to triggering these reactions, the catalytic coating having the iron-containing material advantageously brings about a reduction in the ignition temperature of the soot, as well.

In this connection, the following reaction equations are produced: 2N0+C−>N₂+C0 ₂ and 2NO₂+2C−>N₂+2CO₂

The effect of the simultaneous nitrogen-oxide reduction and the soot oxidation in the exhaust gas of the internal combustion engine, which results in particularly effective purification of the exhaust gas and therefore allows more stringent exhaust-gas limiting values to be met, should be particularly emphasized.

Since the supporting material is an aluminosilicate or a silicon oxide, a very fine distribution of the iron-containing material present on the surface of the supporting material is achieved, which means that a considerable increase in the reactivity is achieved.

Particularly good results regarding the soot-NO_(x), conversion may be obtained, when a zeolite is used as a supporting material.

However, as an alternative, a silicon oxide, whose skeletal structure is of the type MCM41 or MCM48, may also be used as a supporting material. Good results regarding the soot-NO_(x) conversion were also achieved with this.

It has proven to be particularly advantageous with regard to the catalytic reactions, when the iron-containing material includes iron oxide. Iron oxide is a highly effective oxidation catalyst for soot and is advantageously nontoxic.

In this connection, it may be particularly advantageous when the iron-containing material is made of up to 100% iron oxide.

As an alternative, a good purifying effect is also to be expected when the iron-containing material includes pure iron.

In this case, it is also analogously conceivable for the iron-containing material to be made of up to 100% pure iron.

Improved reaction of the exhaust-gas components and, therefore, a particularly good purifying effect was able to be observed when the catalytically active coating included a noble metal.

In this context, the noble metals platinum and, in particular, palladium have proven to be particularly effective.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an internal combustion engine having an exhaust pipe, in which a device of the present invention for purifying the exhaust gas of the internal combustion engine is situated.

FIG. 2 shows a schematic representation of the layer construction of a preferred embodiment according to the present invention.

DETAILED DESCRIPTION

An internal combustion engine 1 is provided with an exhaust system 2 that has an exhaust pipe 2 a, through which the exhaust gases produced in internal combustion engine 1 in a manner known per se are discharged. A device 3 for purifying the exhaust gases of internal combustion engine 1 is situated in exhaust pipe 2 a, the device being described in more detail in the following. Internal combustion engine 1 is preferably an engine, which functions according to the diesel principle, and in whose exhaust gas soot particles are contained in addition to other pollutants.

Device 3 includes a particle filter 4, which is represented in a highly schematic manner and is preferably made of ceramic, such as silicon carbide, but may also be made of aluminum oxide or another suitable material. For its part, particle filter 4 has a plurality of intake ports 5 and exhaust ports 6, which are alternately closed. Therefore, it is a two-way duct system. Alternatively, an open system having any duct shape and geometry would also be possible. Intake ports 5 and exhaust ports 6 are separated from each other by specific walls 7 indicated by dashed lines, which means that the exhaust gases must flow through walls 7 in order to travel from intake ports 5 into exhaust ports 6 and leave particle filter 4 in this manner. To this end, the material of walls 7 of particle filter 4 is designed to be porous in a manner known per se, so that the gaseous exhaust-gas components may pass through walls 7, but the soot particles remain at the same and are deposited.

As can be seen in the schematic representation according to FIG. 2, particle filter 4 or walls 7 forming the same are provided with a catalytically active coating 8, which includes a supporting material 9 and an iron-containing material 10, which is joined to supporting material 9 and is present on the surface of the same. Supporting material 9 of catalytically active coating 8 is joined to particle filter 4 by an adhesive agent 1, preferably silicon oxide. For example, aluminum oxide (Al₂O₃), titanium oxide (TiO₂), cerium oxide (CeO₂), zirconium oxide (ZrO₂), or another suitable material may also be used as an adhesive agent 11, which, on one side, bonds itself to the material of particle filter 4 and, on the other side, gives sufficient support to catalytically active coating 8. Methods, which are known per se and are therefore not explained below in further detail, may be used for joining catalytically active coating 8 to particle filter 4 via adhesive agent 11. It is also possible to dispense with adhesive agent 11. Of course, the layer thicknesses represented in FIG. 2 are to be regarded as purely exemplary.

In one specific embodiment of device 3, iron-containing material 10 may include iron oxide; in this connection, it is also possible for iron-containing material 10 to be made of up to 100% iron oxide. As an alternative, it is equally possible for iron-containing material 10 to include pure iron or to be made of up to 100% pure iron. In addition, a mixture of iron oxide and pure iron for forming iron-containing material 10 is also possible. Furthermore, titanium, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, tungsten, and/or rhenium may be included in iron-containing material 10, iron oxide or pure iron always forming the largest part of iron-containing material 10.

The ion-exchange method known per se may be used for joining iron-containing material 7 to supporting material 9; however, it is also possible to join supporting material 9 to iron-containing material 10 with the aid of a coating method.

In the present case, catalytically active coating 8 has, in addition to supporting material 9 and iron-containing material 10, a noble metal 12, which, in the represented case, is applied to catalytically active coating 8 as an additional layer. It is also possible to distribute noble metal 12 in catalytically active coating 8 in a manner not shown. Palladium or platinum is preferably used as a noble metal 12, but ruthenium, rhodium, silver, osmium, iridium, or gold may also be used. Noble metal 12 may be present as an oxide or as a pure element.

Supporting material 9 is preferably made of an amorphous or crystalline aluminosilicate, for example a β-zeolite, a zeolite of the type Y, or a zeolite of the type ZSM5. This porous supporting material 9 having a very large surface area is modified, using iron-containing material 10, so that iron-containing material 10 is finely distributed over at least nearly the entire surface of supporting material 9. A crystalline β-zeolite has proven to be particularly suitable in practice, especially since it does not decompose, even after a long period of time in which it is exposed to the exhaust gas, and it produces, especially with iron-containing material 10, an exceptionally good efficacy of the catalytically active coating 8. It would also be alternatively possible to use amorphous silicon oxide (SiO₂) for supporting material 9, its skeletal structure being able to be of type MCM41, for example.

The mode of operation of device 3 is as follows: the soot particles contained in the exhaust gas deposit on particle filter 4 and reduce the NO₂ and NO molecules contained in the exhaust gas to N₂ molecules by the action of catalytically active coating 8, the carbon essentially forming the soot particles being simultaneously oxidized to form CO₂. The following reaction equations, or at least one of the same, apply in this case: 2N0+C−>N₂+CO₂ and 2NO₂+2C−>N₂+2CO₂

This means that only a considerably reduced amount of NO_(x) molecules, and essentially only N₂ molecules, are contained in the exhaust gas leaving device 3, and that the soot particles are simultaneously deposited on particle filter 4 and subsequently oxidized by NO and NO₂. The action of iron-containing material 7 in catalytically active coating 8 allows the described reactions to already proceed at temperatures of app. 220° C., so that is not necessary to position device 3 particularly close to internal combustion engine 1 or to introduce additional reducing agents into exhaust pipe 2 a. Consequently, it is possible to remove the two pollutants NO_(x) and soot from the exhaust gas of internal combustion engine 1, using a single device 3.

In FIG. 1, it is also shown that device 3 may be coupled to an additional, commercially obtainable, upstream, e.g. platinum-based and/or palladium-based, oxidation catalytic converter 13, in order to produce the more reactive NO₂ from the NO present in the exhaust gas. A further task of oxidation catalytic converter 13 may be to oxidize hydrocarbons and CO. Since hydrocarbons could particularly be stored in the zeolite, the risk of deactivating the zeolite is prevented in this manner. 

1-19. (canceled)
 20. A device for purifying an exhaust gas of an internal combustion engine, comprising: a particle filter provided with a catalytically active coating, the catalytically active coating having a supporting material and an iron-containing material that is joined to the supporting material and is at least present on the surface of the same, and the supporting material being an aluminosilicate or a silicon oxide.
 21. The device as recited in claim 20, wherein the supporting material is a zeolite.
 22. The device as recited in claim 20, wherein the supporting material is a silicon oxide, whose skeletal structure is of the type MCM41 or MCM48.
 23. The device as recited in claim 20, wherein the iron-containing material includes iron oxide.
 24. The device as recited in claim 23, wherein the iron-containing material is up to 100% iron oxide.
 25. The device as recited in claim 20, wherein the iron-containing material includes pure iron.
 26. The device as recited in claim 25, wherein the iron-containing material is up to 100% pure iron.
 27. The device as recited in claim 20, wherein the iron-containing material is joined to the supporting material by coating.
 28. The device as recited in claim 20, wherein the iron-containing material is applied to the supporting material by ion exchange.
 29. The device as recited in claim 20, wherein the catalytically active coating includes a noble metal.
 30. The device as recited in claim 29, wherein the noble metal is applied to the catalytically active coating as an additional layer.
 31. The device as recited in claim 29, wherein the noble metal is distributed in the catalytically active coating.
 32. The device as recited in claim 29, wherein the noble metal is platinum or palladium.
 33. The device as recited in claim 21, wherein the zeolite is a β-zeolite.
 34. The device as recited in claim 20, wherein the supporting material is joined to the particle filter with the aid of an adhesive agent.
 35. The device as recited in claim 34, wherein the adhesive agent includes silicon oxide, aluminum oxide, cerium oxide, zirconium oxide, or titanium oxide.
 36. The device as recited in claim 20, wherein the particle filter is made of ceramic or of metal, having a two-way duct system or an open system.
 37. An exhaust system for an internal combustion engine, comprising: an exhaust pipe; and a device situated in the exhaust pipe and for purifying an exhaust gas of an internal combustion engine, the device including: a particle filter provided with a catalytically active coating, the catalytically active coating having a supporting material and an iron-containing material that is joined to the supporting material and is at least present on the surface of the same, and the supporting material being an aluminosilicate or a silicon oxide.
 38. The exhaust system as recited in claim 37, wherein the device is coupled to an upstream oxidation catalytic converter. 